Implants and Methods of Use

ABSTRACT

Implant devices, and method of using the same, are provided. The implant devices have circular, or oblong, articular ends. The articular ends have a convex upper face and a concave lower face, the convex upper face blending to the concave lower face, and the concave lower face having a curvature less than the curvature of the convex upper face. The implant devices further have a stem extending from the concave lower face away from the upper face, the stem having a maximum radius at the convex lower face and tapering to lesser radius along the length of the stem.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 12/074,770, filed Mar. 6, 2008.

FIELD OF THE INVENTION

This invention relates generally to devices and methods for the repairof articular cartilage defects. More particularly, this inventionrelates to implants that serve as a replacement for diseased cartilagein joints such as human knees, hips and shoulders.

BACKGROUND OF THE INVENTION

Cartilage acts as a pad between bones to reduce friction and prevent thebones from grinding against one another. Cartilage covers the articularsurface of many, if not all, joints in the body. The smoothness andthickness of the cartilage are factors that determine the load-bearingcharacteristics and mobility of the joints. Over time, due to injury orheredity, however, lesions such as fissures, cracks or crazes can formin the cartilage. In some cases, osteochondral, the lesion penetrates tothe subchondral surface of the bone. In other cases, chondral, thelesion does not penetrate to the subchondral surface of the bone. In anyevent, lesions generally do not repair themselves—and if any repair ismade it is insufficient to heal—leading to significant pain anddisability, either acutely or over time.

One approach for regenerating new cartilage is autologous chondrocytetransplantation. However, this technique is complex and relativelycostly. Other techniques, aimed at repair instead of regeneration,include debridement, lavage, microfracturing, drilling, and abrasionarthroplasty. These procedures generally involve penetrating the regionof vascularization in the subchondral bone with an instrument untilbleeding occurs. Formation of a fibrin clot differentiates intofibrocartilage, which then covers the defect site. Some have found,however, that the resulting repair tissue is relatively weak,disorganized, and lacks the biomechanical properties of normal hyalinecartilage that typically covers the bone ends. Additionally, thistechnique can generally only be used on chondral defects in the presenceof normal joint congruity.

An alternative approach has been to undergo a total replacement of thejoint. Such total replacements, however, are costly, high risk, andinvolve a long recovery time. Accordingly, there is a need foralternative treatments.

SUMMARY OF THE INVENTION Definitions

In various illustrative embodiments, the terms “vertical axis” or“vertical” mean a direction from the top of a three-dimensional objectto the bottom of the three-dimensional object.

In various illustrative embodiments, the term “yaw” means a direction ofrotation around the vertical axis.

In various illustrative embodiments, the terms “horizontal axis” or“horizontal” mean a direction from right of the three-dimensional objectto the left of the three-dimensional object.

In various illustrative embodiments, the term “pitch” means a directionof rotation around the horizontal axis.

In various illustrative embodiments, the terms “depth axis” or “depth”mean a direction from the front of the three-dimensional object to theback of the three-dimensional object.

In various illustrative embodiments, the term “roll” means a directionof rotation around the depth axis.

In various illustrative embodiments, the term “spherical radius” meansthe curvature of a surface formed by a sphere having a particularradius. Accordingly, when a surface is referred to as having a sphericalradius, it is meant that the surface has a curvature equal to thecurvature of the surface of a sphere having a particular radius.

In various illustrative embodiments, the term “circular yaw radius”means the maximum curvature about yaw of a surface formed by a circlehaving a particular radius rotated about yaw.

In various illustrative embodiments, the term “circular roll radius”means the maximum curvature about roll of a surface formed by a circlehaving a particular radius rotated about roll.

In various illustrative embodiments, the term “circular pitch radius”means the maximum curvature about pitch of a surface formed by a circlehaving a particular radius rotated about pitch.

In various illustrative embodiments, the term “oval” means twosemi-circles connected by two straight line segments that do notintersect and that each are tangent to each semi-circle, alternativelythe term “oval” means an oblong three-dimensional closed curve having nostraight segments.

In various illustrative embodiments, the term “torus” means the surfaceof a toriod.

In various illustrative embodiments, the term “tubular radius” refers tothe radius of the tube of a torus, as opposed to the radius from thecenter of the torus to the center of the tube.

In various illustrative embodiments, geometric terms such as “oval”,“circle”, “sphere”, “cylinder”, and the like are used as references andfor clarity of understanding, as would be understood by one of ordinaryskill in the art. Accordingly, these terms should not be limited tostrict Euclidean standards.

Various illustrating embodiments of the present invention provides animplant, preferably for use in human joints, including knees. Inaccordance with one aspect of an illustrating embodiment of the presentinvention an implant is provided which includes an articular end havinga circular perimeter, a convex upper face, and a concave lower face. Theconvex upper face may have a spherical radius and the concave lower facemay have a spherical radius. The implant additionally may include a stemextending from the concave lower face away from the convex upper facealong a vertical axis. The stem may have a circular perimeter which is amaximum at the intersection of the stem and the concave lower face, andwhich decreases to a lesser circular perimeter along the vertical axisof the stem. Preferably, the maximum stem circular perimeter is lessthan the articular end circular perimeter.

In accordance with another aspect of an illustrating embodiment of thepresent invention, an implant is provided, which includes an articularend having an oval perimeter, a convex upper face and a concave lowerface. The convex upper face of the oval articular end may have a firstcircular pitch radius and a first circular roll radius. The concavelower face of the oval articular end may have a spherical radius.Preferably, the convex upper face blends into a rim, wherein at leastfirst and second portions of the rim extend at least a first distancealong the vertical axis and third and fourth portions of the rim taperinward along the vertical axis, and the rim further blends into theconcave lower face. The implant further may include a stem extendingfrom the concave lower face away from the convex upper face. Preferably,the stem has an oval shaped perimeter in a plane perpendicular to thevertical axis.

Those skilled in the art will further appreciate the above-mentionedadvantages and superior features of the invention together with otherimportant aspects thereof upon reading the detailed description whichfollows in conjunction with the drawings, in which like parts are givenlike reference numerals, and the vertical, horizontal and depthorientations of a given embodiment are specified explicitly in at leastone drawing of the embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figures are not necessarily to scale and certain features ofthe invention may be shown exaggerated in scale or in somewhat schematicform in the interest of clarity and conciseness, wherein:

FIG. 1 is a front view of one embodiment of an implant;

FIG. 2 is a top-down view of the embodiment of FIG. 1;

FIG. 3 is a cut-away view of the implant of FIG. 1 taken along line 3-3,

FIG. 4 is an exploded view of a portion of the front view of FIG. 1;

FIG. 5 is a front view of an alternative embodiment of an implant;

FIG. 6 is a side view of the embodiment of FIG. 5;

FIG. 7 is a top-down view of the embodiment of FIG. 6;

FIG. 8 is a cut-away view of the implant of FIG. 5 taken along line 8-8;

FIG. 9 is a cut-away view of the implant of FIG. 6 taken along line 9-9;and

FIG. 10 is an exploded view of a portion of the cut-away view of FIG. 8.

DISCLOSURE OF ALTERNATIVE EMBODIMENTS

FIG. 1 is an illustrative embodiment of an implant 100, in which thevertical, V, horizontal, H, and depth, D, orientations of thisembodiment are depicted. The implant 100 preferably has an articular end105 and a stem 130. The articular end 105 may be a disk of uniformthickness in the vertical or a cylinder of uniform length in thevertical. Preferably, the articular end 105 has a convex upper face 110,which blends 125 into, and is bounded by, a circular perimeter portion120, which—after some length—itself blends 125 into a concave lower face115.

In this embodiment, the circular pitch radius of the convex upper face110 is about the same as the circular roll radius of the convex upperface 110. The circular pitch radius and the circular roll radius of theconvex upper face 110 may be from about 25 to about 40 millimeters,alternatively from about 30 to about 35 millimeters, alternatively fromabout 28 to about 32 millimeters. In an embodiment, the circular pitchradius and the circular roll radius of the convex upper face 110 areapproximately equal, i.e., the convex upper face 110 may have aspherical radius. The convex upper face 110 may blend, as at 125, intothe circular perimeter 120, with the blend 125 having an edge radius offrom about 0.1 millimeters to about 1 millimeter. Alternatively, theblend may be about 0.5 millimeters.

The circular perimeter 120 may extend some distance along the verticalaxis, thereby forming a cylinder between the convex upper face 110 andthe concave lower face 115. The length of the cylinder formed by thecircular perimeter 120 may range from about one millimeter to about 5millimeters, and alternatively from about 2 millimeters to about 3millimeters. Referring to FIG. 2, the diameter of the circular perimeter120 may be of any length, and may range from about 10 millimeters toabout 30 millimeters, alternatively from about 12 millimeters to about20 millimeters. Alternative diameters of the circular perimeter 120include about 12.5 millimeters, about 15 millimeters, about 17.5millimeters, and about 20 millimeters.

In alternative embodiments, implants 100 having circular perimeters withrelatively large diameters may have convex upper faces with relativelysmall spherical radii. In an embodiment, relatively large diameters ofcircular perimeters are greater than about 17 millimeters. In anembodiment, relatively small spherical radii of convex upper faces areless than about 30 millimeters. Conversely, in alternative embodiments,implants 100 having circular perimeters with relatively small diametersmay have convex upper faces with relatively large spherical radii. In anembodiment, relatively small diameters of circular perimeters are lessthan about 17 millimeters. In an embodiment, relatively large sphericalradii of convex upper faces are greater than about 30 millimeters. Inembodiments wherein the diameter of the circular perimeter 120 rangesfrom about 10 millimeters to about 15 millimeters, the convex upper face110 may have a spherical radius ranging from about 30 millimeters toabout 40 millimeters, preferably about 32 millimeters. In embodimentswherein the diameter of the circular perimeter 120 ranges from about17.5 millimeters to about 20 millimeters the convex upper face 110 mayhave a spherical radius ranging from about 25 millimeters to about 30millimeters, preferably about 28 millimeters. Continuing with respect toFIG. 1, in a further embodiment, the circular perimeter 120 may blend125 into the concave lower face 115. Alternatively, the blend 125 is anedge radius of from about 0.1 millimeters to about 1 millimeter,alternatively about 0.5 millimeters.

The circular pitch radius of the concave lower face 115 may be about thesame as the circular roll radius of the concave lower face 115. In thisembodiment, the circular pitch radius and the circular roll radius ofthe concave lower face 115 may be of any length, and may range fromabout 20 to about 40 millimeters, alternatively from about 25 to about35 millimeters. An alternative circular pitch radius and circular rollradius of the concave lower face 115 is about 29.5 millimeters. Inembodiments wherein the diameter of the circular perimeter 120 isrelatively small, the circular pitch and roll radii of the convex upperface 110 may be greater than the circular pitch and roll radii of theconcave lower face 115. Further, in embodiments wherein the diameter ofthe circular perimeter 120 is relatively small, the convex upper face110 may have a spherical radius of about 32 millimeters and the concavelower face may have a spherical radius of about 29.5 millimeters. Inembodiments wherein the diameter of the circular perimeter 120 isrelatively large, the circular pitch and roll radii of the convex upperface 110 may be lesser than the circular pitch and roll radii of theconcave lower face 115. Further, in an embodiment wherein the diameterof the circular perimeter 120 is relatively large, the convex upper face110 may have a spherical radius of about 28 millimeters and the concavelower face may have a spherical radius of about 29.5 millimeters.

In an embodiment, the circular pitch and roll radii of the convex upperface 110 are about concentric with the circular pitch and roll radii ofthe concave lower face 115. In an embodiment, wherein the diameter ofthe circular perimeter 120 is relatively small, the convex upper face110 and the concave lower face 115 may have spherical radii of about 32millimeters and about 29.5 millimeters, respectively. In thisembodiment, spherical radii of the convex upper face 110 and the concavelower face 115 may be approximately concentric, and the centers of thespherical radii of the convex upper face 110 and the concave lower face115 both may lie on the central vertical axis of symmetry of the implant100, at the same point or nearly the same point. In an embodiment,wherein the diameter of the circular perimeter 120 is relatively large,the convex upper face 110 and the concave lower face 115 may havespherical radii of about 28 millimeters and about 29.5 millimeters,respectively. In this embodiment, the convex upper face 100 and theconcave lower face 115 may not be concentric and may be separated by adistance along the central vertical axis of symmetry of the implant 100and the respective centers of the spherical radii of the convex upperface 110 and the concave lower face 115 may lie on the central verticalaxis of symmetry of the implant 100. The distance of separation betweenthe convex upper face 100 and the concave lower face 115 along thecentral vertical axis of symmetry may range from about 2 millimeters toabout 4 millimeters and may alternatively be about 2.5 millimeters.

A stem 130 may extend from the concave lower face 115 in the verticaldirection away from the convex upper face 110. Alternatively, the stem130 blends 150 into the concave lower face 115. Alternatively, the blend150 is a fillet radius of from about 0.1 millimeters to about 1.5millimeters, alternatively about 0.8 millimeters. The center of the stem130 about its yaw may be concentric with the center of the circularperimeter 120 about its yaw. The stem 130 may have a maximum stem yawradius at the intersection of the stern 130 and the concave lower face115. The maximum stem yaw radius may be less than the circular perimeter120 yaw radius. In this embodiment, the stem yaw radius tapers from itsmaximum to a lesser stem yaw radius along the vertical length of thestem 130. In this embodiment, the stem 130 may be generally conicalalong its entire vertical length. In a still further embodiment, theoverall vertical length of the stem 130 may be at least 50% of thediameter of the circular perimeter 120.

Alternatively, the stem 130 has a cylindrical portion 135 extending fromthe concave lower face 115 in the vertical direction away from theconcave upper face 110, and a conical portion 140 further extending fromthe end of the cylindrical portion 135 in the vertical direction awayfrom the concave upper face 110. The cylindrical portion 135 may be ofany length and may have a length along its vertical axis of from aboutone millimeter to about 5 millimeters, alternatively from about 2millimeters to about 3 millimeters. The cylindrical portion 135 may havea circular yaw radius of any length, alternatively from about 1millimeter to about 5 millimeters, alternatively from about 2millimeters to about 4 millimeters. More preferred circular yaw radii ofthe cylindrical portion 135 include about 2.75 millimeters, about 3.125millimeters, about 3.5 millimeters, and about 3.875 millimeters. Withoutwishing to be bound by the theory, the cylindrical portion 135 ispreferable as it allows for ease of manufacturing, i.e., it provides aphysical structure to clamp during manufacturing.

The conical portion 140 may be of any length and preferably ranges alongits vertical length from about 2 millimeters to about 15 millimeters,alternatively from about 5 millimeters to about 15 millimeters, andalternatively from about 8.5 millimeters to about 11 millimeters. Inthis embodiment, the maximum circular yaw radius of the conical portion140 may be located at the intersection between the conical portion 140and the cylindrical portion 135, and is equal to the circular yaw radiusof the cylindrical portion 135. The conical portion 140 may have a yawradii that decreases from the maximum to a minimum along its verticalaxis in the direction away from the upper convex face 110. The circularyaw radii of the conical portion 140 may be of any length, and may rangefrom about one millimeter to about 5 millimeters, alternatively fromabout 2 millimeters to about 3 millimeters.

With respect to FIG. 4, the conical portion 140 may have circumferentialgrooves 145 around its perimeter. The shape of the circumferentialgrooves 145 may be defined by a partial torus having a tubular radius ofany length, and may range from about 0.25 millimeters to about 2millimeters, more preferably from about 0.5 millimeters to about 1millimeter, alternatively about 1 millimeter. The circumferentialgrooves 145 may be spaced apart at any distance, and may be spaced apartat a distance from about 1 to about 3 millimeters from each other alongthe vertical, alternatively from about 2 to about 2.5 millimeters.

FIGS. 5 and 6 illustrate an alternative embodiment of an implant 200.The vertical, V, horizontal, H, and depth, D, orientations of thisalternative embodiment of the implant 200 are depicted in FIG. 5. Theimplant 200 may have an articular end 205 and a stem 230. The articularend 205 may be an oval column of uniform thickness in the verticalhaving planar surfaces at its upper and lower faces. Alternatively,however, with respect to FIGS. 5, 6, and 7, the articular end 205 has aconvex upper face 210, which blends, as at, 225 into, and is bounded by,an oval perimeter 220, which—after some length—itself blends 225 into aconcave lower face 215. The blends 225 may have an edge radius fromabout 0.1 millimeters to about 1 millimeter. Alternatively the blends225 may have an edge radius of about 0.5 millimeters.

With respect to FIG. 5, and in an embodiment the maximum length of thearticular end 205 along the horizontal axis may be any length and mayrange from about 15 millimeters to about 40 millimeters, alternativelyfrom about 20 millimeters to about 35 millimeters. Preferred maximumlengths of the articular end 205 along the horizontal axis include about20 millimeters, about 22.5 millimeters, about 25 millimeters, about 27.5millimeters, and about 30 millimeters. The maximum length of thearticular end 205 along the depth axis may be of any length and mayrange from about 10 millimeters to about 30 millimeters, alternativelyfrom about 15 millimeters to about 25 millimeters. Alternative maximumlengths of the articular end 205 along the depth axis include about 15millimeters, about 17.5 millimeters, and about 20 millimeters. In thisembodiment the maximum length of the implant 200 along the vertical axismay be of any length and may range from about 10 millimeters to about 35millimeters, alternatively from about 10 millimeters to about 20millimeters. In one illustrative embodiment, the maximum length of theimplant 200 along the vertical axis is about 15 millimeters.

With respect to FIG. 5, the circular pitch radius of the convex upperface 210 may be of any length and may range from about 15 millimeters toabout 30 millimeters, alternatively from about 20 millimeters to about25 millimeters. An alternative length of the circular pitch radius ofthe convex upper face 210 is about 22 millimeters. The circular rollradius of the convex upper face 210 may be of any length and may rangefrom about 20 millimeters to about 40 millimeters, alternatively fromabout 25 millimeters to about 35 millimeters. An alterative length ofthe circular roll radius of the convex upper face 210 is about 32millimeters. The convex upper face 210 may have a circular pitch radiusand a circular roll radius, which may be different values.

In an embodiment the curvature of the concave lower face 215 may bedescribed as a single spherical radius. In an embodiment, the sphericalradius of the concave lower face 215 ranges from about 20 to about 40millimeters, alternatively from about 25 to about 35 millimeters,alternatively about 29.5 millimeters.

The stem 230 may have two portions, which may be both generally oval incross-section in planes perpendicular to the vertical axis. The firstportion 235 may extend from the concave lower face 215 a length alongthe vertical in a direction away from the convex upper face 210, and thesecond portion 240 extends from the end of the first portion 235 alength along the vertical in a direction away from the convex upper face210. The stem 230 may blend 250 into the concave lower face 215 of thearticular end 205. In an embodiment, the blend 250 is a fillet radius offrom about 0.1 millimeters to about 1.5 millimeters, alternatively about0.8 millimeters. The first portion 235 may be of a uniform length alongthe depth and of a decreasing length along the horizontal as it extendsin the vertical. The first portion 235 may be of any length along thedepth and may range from about 2 millimeters to about 25 millimeters,alternatively from about 5 millimeters to about 20 millimeters,alternatively from about 5 millimeters to about 10 millimeters. Analternative length along the depth of the first portion 235 is about6.25 millimeters. The length along the horizontal of the first portion235 may decrease from a maximum length at the intersection with theconcave lower face 215 to a lesser length as it extends along thevertical. The maximum length of the first portion 235 along thehorizontal may be of any length, and may range from about 5 millimetersto about 20 millimeters, alternatively from about 10 millimeters toabout 15 millimeters. With respect to FIG. 8, the first portion 235 maybe of any length in the vertical direction, and preferably ranges fromabout 2 millimeters to about 10 millimeters, alternatively from about 2millimeters to about 8 millimeters; an alternative length of the firstportion 235 in the vertical direction is about 3.6 millimeters. Withoutwishing to be bound by the theory, the first portion 235 is preferableas it allows for ease of manufacturing, i.e., it provides a physicalstructure to clamp during manufacturing.

The second portion 240 may decrease from a maximum horizontal length tolesser horizontal length as it extends in the vertical direction. Themaximum horizontal length of the second portion 240 may be the same asthe horizontal length of the first portion 235 at the intersection ofthe first 235 and second 240 portions. The second portion may decreasefrom a maximum length along the depth to lesser length along the depthas it extends in the vertical direction. The maximum length along thedepth of the second portion 240 may be the same as the length along thedepth of the first portion 235 at the intersection of the first 235 andsecond 240 portions, and thus may range in value as recited above withrespect to the depth length of the first portion 235. With respect toFIG. 8, the second portion 240 may be of any length along the verticaldirection, and may range from about 2 millimeters to about 25millimeters, alternatively from about 5 millimeters to about 20millimeters, alternatively from about 5 millimeters to about 10millimeters; an alternative length of the second portion 240 along thevertical direction is about 9.1 millimeters.

As shown in FIG. 10, the second portion 240 may have grooves 245 aboutits perimeter. The shape of the grooves 245 may be defined by a partial,oval, non-planar torus having a tubular radius of any length,alternatively from about 0.25 millimeters to about 2 millimeters,alternatively from about 0.5 millimeters to about 1 millimeter. Thetubular radius of the partial, oval, non-planar torus of the grooves 245may be about 1 millimeter. Alternatively the grooves 245 are spacedapart at any distance, and may be from about 1 to about 3 millimetersfrom each other along the vertical, alternatively from about 2 to about2.5 millimeters.

The implant 100 or 200 may be manufactured from a variety of suitablematerials, including any of the following, individually or incombination, graphite, pyrocarbon, ceramic, aluminum oxide, siliconenitride, silicone carbide or zirconium oxide; metal and metal alloys,e.g., CO—R—W—Ni, Co—Cr—Mo, CoCr alloys, CoCr molybdenum alloys, Cr—Ni—Mnalloys; powder metal alloys, 316L or other stainless steels, Ti and Tialloys including Ti 6A1-4V ELI; polymers, e.g., polyurethane,polyethylene, polypropylene, thermoplastic elastomers,polyaryletherketones such as polyetherehterketone (PEEK) orpolyetherketoneketone (PEKK); biomaterials such as polycaprolactone; anddiffusion hardened materials such as Ti—13-13, zirconium and niobium.Moreover, the implant 100 or 200 may be coated with a variety ofsuitable materials, including any of the following, individually or incombination, porous coating systems on bone-contacting surfaces,hydrophilic coatings on load-bearing surfaces, hydroxyapaite coatings onbone-contacting surfaces, and tri-calcium phosphate on bone-contactingsurfaces. Other suitable coatings include growth factors and otherbiological agents such as bone morphogenetic proteins (BMP's),transforming growth factor beta, among others. Additionally, componentsof the invention may be molded or cast, hand-fabricated or machined.

In one illustrative embodiment, the implant 100 or 200 is composed ofgraphite and pyrocarbon. The implant 100 or 200 may be graphite and mayinclude a coating of pyrocarbon. The pyrocarbon coating may have anaverage thickness of from about 100 to about 1000 microns, alternativelyfrom about 200 microns to about 500 microns, alternatively from about250 to about 500 microns, alternatively about 350 microns. Thepyrocarbon coating may have an elastic modulus from about 15 gigapascals(“GPa”) to about 22 GPa, alternatively about 20 GPa. The pyrocarboncoating may further have a strength of at least 200 megapascals (“MPa”),alternatively at least about 300 MPa, alternatively at least about 400MPa. The pyrocarbon elastic modulus and strength may be tested using afour-point bend, third-point-loading substrated specimens of dimensions25 millimeters by 6 millimeters by 0.4 millimeters. In an embodiment,the pyrocarbon is pyrolytic carbon as described in Pure PyrolyticCarbon: Preparation and Properties of a New Material, On-X Carbon forMechanical Heart Valve Prostheses, Ely et al, J. Heart Valve Dis., Vol.7, No. 6, A00534 (November 1998), alternatively pyrocarbon is pyrolyticcarbon as described in the before-mentioned J. Heart Valve Dis.publication, but includes additional silicon.

The above-described implants may be used to repair damaged articularcartilage in humans, including knees, wrists, elbows, shoulders, and thelike joints. In an illustrative method, a patient having articularcartilage damage is identified. The patient is fully informed of therisks associated of surgery, and consents to the same. An incision maybe made near the damaged articular cartilage. The lesion to be repairedis identified, and an implant having dimensions compatible with thelesion is selected. The implant may be slightly smaller or slightlylarger than the lesion. In these embodiments, the implant is from about0.1 percent to about 20 percent smaller or larger than the lesion. Ahole is then formed, i.e., drilled, punched, or broached, through thecartilage and the subchondral bone into the cancellous bone. Preferably,the dimensions of the hole are slightly less than the horizontal anddepth dimensions of the stem of the implant. This may be achieved, forexample, by using a tapered dill bit. Preferably the minimum length ofthe hole is equal to or slightly greater than the length of the stem ofthe implant, along the vertical. An amount of healthy and damagedcartilage may be removed near the lesion so that the lower portion ofthe implant's articular end may rest against the patient's bone. In thismanner, however, it is preferable to remove as little healthy cartilageas possible. The stem of the implant may be inserted into the hole, andthe lower portion of the implant's articular end may rest against thebone. The incision is then sutured by any of several known methods.

While specific alternatives to steps of the invention have beendescribed herein, additional alternatives not specifically disclosed butknown in the art are intended to fall within the scope of the invention.Thus, it is understood that other applications of the present inventionwill be apparent to those skilled in the art upon reading the describedembodiment and after consideration of the appended claims and drawings.

1) An implant comprising: an articular end having a circular perimeterapproximately defined by a diameter, a convex upper face, and a concavelower face, the convex upper face having a first spherical radius andthe concave lower face having a second spherical radius, wherein thefirst spherical radius is relatively small if the diameter is relativelylarge; and a stem extending from the concave lower face away from theconvex upper face along a vertical axis, the stem having a maximum stemcircular perimeter at the intersection of the stem and the concave lowerface, the maximum stem circular perimeter less than the articular endcircular perimeter. 2) The implant of claim 1, wherein the stem circularperimeter decreases from a maximum stem circular perimeter to a lesserstem circular perimeter along the vertical axis of the stem. 3) Theimplant of claim 1, wherein the stem has a cylindrical portion extendingfrom the concave lower face away from the convex upper face along thevertical axis, and a conical portion extending from the cylindricalportion away from the convex upper face along the vertical axis. 4) Theimplant of claim 3, wherein the cylindrical portion has a length rangingfrom about one millimeter to about five millimeters; and the conicalportion has a length ranging from about two millimeters to about fifteenmillimeters. 5) The implant of claim 1, wherein the diameter ranges fromabout 17.5 millimeters to about 20 millimeters and the first sphericalradius ranges from about 25 millimeters to about 30 millimeters,preferably about 28 millimeters. 6) The implant of claim 1, wherein thefirst spherical radius is relatively large if the diameter is relativelysmall. 7) The implant of claim 6, wherein the diameter ranges from about10 millimeters to about 15 millimeters and the first spherical radiusranges from about 30 millimeters to about 40 millimeters, preferablyabout 32 millimeters. 8) The implant of claim 1, wherein the firstspherical radius is lesser than the second spherical radius if thediameter is relatively large. 9) The implant of claim 8, wherein thefirst spherical radius is about 28 millimeters, the second sphericalradius is about 29.5 millimeters and the diameter is greater than about17 millimeters. 10) The implant of claim 1, wherein the first sphericalradius is greater than the second spherical radius if the diameter isrelatively small. 11) The implant of claim 10, wherein the firstspherical radius is about 32 millimeters, the second spherical radius isabout 29.5 millimeters and the diameter is less than about 17millimeters. 12) The implant of claim 1, wherein the diameter isrelatively large, the first spherical radius is about 28 millimeters,the second spherical radius is about 29.5, the convex upper face and theconcave lower face are separated by about 2.5 millimeters along avertical axis of symmetry of the implant, and the center of curvature ofthe first spherical radius and a center of curvature of the secondspherical radius align with the vertical axis of symmetry of theimplant. 13) The implant of claim 1, wherein the diameter is relativelysmall, the first spherical radius is about 32 millimeters, the secondspherical radius is about 29.5 and the first spherical radius is aboutconcentric with the second spherical radius. 14) The implant of claim 3,wherein a portion of the conical portion of the stem is comprised ofcircumferential grooves. 15) The implant of claim 14, wherein thecircumferential grooves are defined by a partial torus having a tubularradius of from about 0.25 millimeters to about 1.5 millimeters, and thecircumferential grooves are spaced apart at a distance of from about 1millimeter to about 3 millimeters from each other. 16) The implant ofclaim 1, wherein the articular end and the stem comprise graphite andpyrocarbon. 17) The implant of claim 16, wherein the articular end andthe stem comprise a graphite core and a pyrocarbon coating, thepyrocarbon coating having an elastic modulus from about 15 GPa to about22 GPa, the pyrocarbon coating having an average thickness ranging fromabout 100 to about 1000 microns. 18) The implant of claim 17, whereinthe pyrocarbon coating has an elastic modulus of about 20 GPa and astrength of at least 400 MPa. 19) The implant of claim 16, wherein theupper face and circular perimeter of the articular end are polished, andthe lower face and stem are coated with hydroxyapatite. 20) An implantcomprising: an articular end having an oval perimeter, a convex upperface, and a concave lower face, the convex upper face having a firstcircular pitch radius and a first circular roll radius, at least aportion of the concave lower face having a spherical radius, the convexupper face blending into a rim, wherein at least a first and secondportion of the rim extends at least a first distance along the verticalaxis and a third and fourth portion of the rim tapers inward along thevertical axis, the rim blending into the concave lower face; and a stemextending from the concave lower face away from the convex upper face,the stem having an oval shaped perimeter in planes perpendicular to thevertical axis. 21) The implant of claim 20, wherein the oval articularend has a maximum length, along the horizontal axis of from about 15millimeters to about 40 millimeters; the oval articular end has amaximum length, along the depth axis, ranging from about 10 millimetersto about 30 millimeters; and the implant has a maximum length along thevertical axis ranging from about 10 millimeters to about 35 millimeters.22) The implant of claim 20, wherein the stem has a first portion and asecond portion, the first portion extending from the lower concave facea length in the vertical direction away from the upper convex face, thesecond portion extending from the first portion a length in the verticaldirection away from the upper convex face, wherein the first portiontapers inward along its horizontal axis in the vertical direction andhas a uniform length along its depth axis in the vertical direction, thesecond portion tapers inward along its horizontal axis and its depthaxis in the vertical direction, the first and second portion blend intoeach other, the length of the first portion along the vertical isselected from the group consisting of 2 millimeters to about 10millimeters and from about 2 millimeters to about 8 millimeters, thelength of the second portion along the vertical is selected from thegroup consisting of from about 2 millimeters to about 25 millimeters,from about 5 millimeters to about 20 millimeters, and from about 5millimeters to about 10 millimeters. 23) The implant of claim 22,wherein the second portion of the stem comprises grooves. 24) Theimplant of claim 23, wherein the grooves are defined by a partial, oval,non-planar torus having a tubular radius of from about 0.25 millimetersto about 1.5 millimeters, and the grooves are spaced apart at a distanceof from about 1 millimeter to about 3 millimeters from each other. 25)The implant of claim 24, wherein the articular end and the stem comprisegraphite and pyrocarbon. 26) The implant of claim 25, wherein thearticular end and the stem comprise a graphite core and a pyrocarboncoating, the pyrocarbon coating having an elastic modulus from about 15GPa to about 22 GPa, the pyrocarbon coating having an average thicknessranging from about 100 to about 1000 microns. 27) The implant of claim26, wherein the pyrocarbon coating has an elastic modulus of about 20GPa and a strength of at least 400 MPa. 28) The implant of claim 27,wherein the upper face and oval perimeter of the articular end arepolished, and the lower face and stem are coated with hydroxyapatite.29) A method of repair of articular cartilage comprising: locatingarticular cartilage having a lesion; utilizing an implant havingdimensions compatible with the lesion, wherein the implant comprises; anarticular end having a circular perimeter approximately defined by adiameter, a convex upper face, and a concave lower face, the convexupper face having a first spherical radius and the concave lower facehaving a second spherical radius, wherein the first spherical radius isrelatively small if the diameter is relatively large; and a stemextending from the concave lower face away from the convex upper facealong a vertical axis, the stem having a maximum stem circular perimeterat the intersection of the stem and the concave lower face, the maximumstem circular perimeter less than the articular end circular perimeterforming a cavity in the cartilage and subchondral bone and cancellousbone; and engaging the implant with the cavity so that the lower surfaceabuts against the prepared subchondral bone and the stem abuts againstthe prepared cancellous bone. 30) The method of claim 29, whereinforming the cavity includes placement of autograft, allograft bone, orvarious bone graft substitute material into the lesion. 31) A method ofrepair of articular cartilage comprising: locating articular cartilagehaving a lesion; utilizing an implant of having dimensions compatiblewith the lesion, wherein the implant comprises; an articular end havingan oval perimeter, a convex upper face, and a concave lower face, theconvex upper face having a first circular pitch radius and a firstcircular roll radius, at least a portion of the concave lower facehaving a spherical radius, the convex upper face blending into a rim,wherein at least a first and second portion of the rim extends at leasta first distance along the vertical axis and a third and fourth portionof the rim tapers inward along the vertical axis, the rim blending intothe concave lower face; and a stem extending from the concave lower faceaway from the convex upper face, the stem having an oval shapedperimeter in planes perpendicular to the vertical axis; forming a cavityin the cartilage and subchondral bone and cancellous bone; and engagingthe implant with the cavity so that the lower surface abuts against theprepared subchondral bone and the stem abuts against the preparedcancellous bone. 32) The method of claim 31, wherein forming the cavityincludes placement of autograft, allograft bone, or various bone graftsubstitute material into the lesion.